8a 6a 3a
6a 6a-13 3a-15
6a-x 6a-13-x 3a-15-x

6a-x+6a-13-x=93 12a-2x=106 6a-x=53 x=6a-53
6a-13-x=20(3a-15-x) 6a-13-x=60a-300-20x 54a-19x=287
54a-19(6a-53)=287 a=12